1. Field of the Invention
The present invention relates to an apparatus for and a method of measuring signal quality, and more particularly, to an apparatus for and a method of measuring signal quality in which the quality of an output signal detected from an RF signal read out from a disk is measured by using signals useable for generating an eye pattern of the output signal.
2. Description of the Related Art
In a system such as a storage medium system or a communication system, when an input signal passes through a channel and is output as an output signal, if external noise is added during channel-transmitting and receiving processes, the output signal passing through the channel has an undesired component and a waveform of the output signal is deformed, causing errors in a process for extracting information from the output signal.
In a conventional signal detection system, signal quality is determined by detecting a jitter value from a received output signal. The jitter value, which represents a percentage variation of the received signal with reference to time, has been widely used to measure signal quality in the storage medium system.
In addition, since a large amount of data is intended to be stored in a physical storage area in a current storage medium system and to be transmitted through a narrow transmission band in a current communication system, a complicated processing algorithm in such an adaptive equalizer and a Viterbi detector has been used for the data detection process rather that a conventional signal processing method using a simple signal polarity detection process.
However, when the conventional method using the jitter value as a criterion for determining signal quality is used in a system performing a complicated signal processing algorithm, the signal quality is not accurately determined because a bit error rate and a detected jitter value have different characteristics.
FIG. 1 is a view illustrating a bit error rate measured in a storage medium system. For this measurement, data were recorded on a 12-cm blu-ray disk with a recording density of 31 gigabytes (GB), and then, so-called “radial and tangential tilts” were added as external noises. After that, the reproducing bit error rate and jitter value were measured. Referring to FIG. 1, a lowest bit error rate was obtained at tilt 0 corresponding to no external noise. As the tilt is increased, the bit error rate increased. In FIG. 1, the expressions for bit error rate, 1.E+00, 1.E−01, 1.E−02 . . . 1.E−06, correspond to 1×10N, where N is 0,−1,−2 . . . −6, respectively.
FIG. 2 is a view illustrating signal quality results obtained by jitter value detection using the same conditions as were used for obtaining the data of FIG. 1. In FIG. 2, a lowest jitter value was obtained at tilt 0, and as the tilt increased, the jitter value increased, similar to the increase in bit error rate shown in FIG. 1. However, at tilts +0.4 and −0.4, the jitter values change differently from the change in bit error rates shown in FIG. 1. Furthermore, at tangential tilts of −0.6 or less and +0.6 or more and at radial tilts of +0.6 or more, the jitter value was not detectable. In other words, the conventional signal quality estimating method using the jitter value does not accurately represent the signal quality in the signal processing method of the high-density storage medium system.
In addition, in the conventional signal quality estimating method using the jitter value measurement, an original signal pattern must be known to measure the quality of output signals.